Wind power is considered one of the cleanest, most environmentally friendly energy sources presently available, and wind turbines have gained increased attention in this regard. A modern wind turbine typically includes a tower, a generator, a gearbox, a nacelle, and one or more rotor blades. The rotor blades capture kinetic energy of wind using known airfoil principles. The rotor blades transmit the kinetic energy in the form of rotational energy so as to turn a shaft coupling the rotor blades to a gearbox, or if a gearbox is not used, directly to the generator. The generator then converts the mechanical energy to electrical energy that may be deployed to a utility grid.
The lift force is generated when the flow from the leading edge to the trailing edge creates a pressure difference between the top and bottom surfaces of the rotor blade. Ideally, the lift force is constant in time to provide the optimal amount of kinetic energy to transmit to the generator. However, as the wind inflow varies in space and time, the rotor blade is subjected to variable inflow conditions and generates variable lift forces resulting in a variation of the blade loading.
The specific lift force depends on a number of factors, such as incoming air flow characteristics (e.g. Reynolds number, wind speed, in-flow atmospheric turbulence) and characteristics of the rotor blade (e.g. airfoil sections, blade chord and thickness, twist distribution, pitch angle, etc.), all resulting in a local angle of attack for the rotor blade that results in a specific lift force.
The variation in the angle of attack during operation of the wind turbine can lead to strongly varying loads acting on the rotor blades as well as the drivetrain components. As such, some wind turbines implement pitching of the rotor blades to mitigate such load variations.
Even still, the art is continuously seeking new and improved systems and methods for reducing such variations in the angle of attack during operation so as to reduce corresponding variations in blade loading. Thus, the present disclosure is directed to a flexible extension connected to wind turbine rotor blades that passively adjusts the airfoil shape of the rotor blade in response to the changing angle of attack.